Facebook and Google's runaway success in capturing large stakes in the digital advertising market comes with responsibilities and they need to do more when curating how advertisements are placed on their platforms, according to WPP Group CEO Martin Sorrell.

Sorrell, whose company owns ad agencies such as the Grey Group and Ogilvy & Mather, was speaking to CNBC at the sidelines of the China Development Forum, where he said the two tech giants have to exert more control over ad placements on behalf of brands, and take more responsibility for it.

"They've always maintained they were sort of digital engineers standing there with their digital spanners, trying to tighten the nuts on their digital pipes and not being responsible for the content that was going through the pipes," said Sorrell.

A key criticism leveled against both Facebook and Google is that the companies are not doing enough to arrest fake news on their platforms.

Pau Barrena | Bloomberg | Getty Images

Sir Martin Sorrell, CEO of WPP

"They can't just say look we're a technology company, we have nothing to do with the content that is appearing on our digital pages," Sorrell said. He added that, as far as placing advertisements was concerned, they have to be held to the same standards as traditional media organizations.

Another concern is that sometimes advertisements are automatically placed alongside objectionable and inappropriate content within those platforms that brands do not have control over.

"The big issue for Google and Facebook is whether they are going to have human editing at this point ... of course they have the profitability. They have the margins to enable them to do it. And this is going to be the big issue — how far are they prepared to go?" Sorrell said, adding they needed to go "significantly far" to arrest these concerns.

A failure to address such issues could see Facebook and Google potentially take hits on ad revenue if brands stop advertising on their platforms. For example, French advertising firm Havas recently pulled all its ad spend from Google and its video platform, YouTube.

The Guardian reported that Havas took the step after talks with Google broke down because the tech giant couldn't provide specific reassurances, policy and guarantees over the filtering and classification of video or display content.

Havas' decision came after the UK government joined organizations including the Guardian, BBC and Transport for London in pulling advertising from Google and YouTube, the Guardian report said.

Sorrell said blanket withdrawals from advertisers across these digital platforms will not solve the problem. Instead, he urged for greater cooperation with the tech giants.

"I think the most constructive way of doing it is getting Google and Facebook to understand the problem, which I think they do, and to get them to step up to control it just like any other media right now would in a traditional sense," he said.